Recently, laminated bus bars have been employed very often in the electric power converters for the conductor in a main wiring circuit between a semiconductor module constituting an inverter section and a power supply for reducing the wiring inductance of the main wiring circuit. The laminated bus bar has a laminate structure formed by laminating conductors for the wiring circuit and insulator plates alternately into a sandwich-shaped unit (Patent Document 1).
As for the semiconductor module in the inverter section described above, the applicant of the present invention has proposed a four-in-one-type three-level IGBT (Insulated Gate Bipolar Transistor) module that includes four sets of semiconductor switching devices, each including an IGBT and an FWD (Free Wheeling Diode) connected in opposite parallel to each other. The four sets of the semiconductor switching devices are housed in a molded resin casing and put together in one package (Patent Document 2).
A conventional structure that employs a laminated bus bar in a main wiring circuit is shown in FIGS. 4(a) through 7 in connection with a single-phase inverter unit of an electric power converter formed of the four-in-one-type IGBT module disclosed in Patent Document 2.
FIG. 4(a) is an oblique view showing the assembly of an inverter unit. FIG. 4(b) is an expanded view of portion A in FIG. 4(a). FIG. 5 is a circuit diagram describing a phase (U phase) of the inverter unit. FIG. 6 is a perspective view showing the external appearance of the inverter unit. FIG. 7 is an enlarged view of the connection terminal section in the laminated bus bar having a conventional structure and employed in the inverter unit shown in FIG. 4(a).
In FIG. 4(a), three-level IGBT module 1, heat sink (radiator fin) 2, and laminated bus bar 3 are shown. Laminated bus bar 3 is wired between IGBT module 1 and filter capacitor (electrolytic capacitor) 4 for a DC power supply to connect IGBT module 1 and filter capacitor 4 to each other.
As shown in FIG. 5, IGBT module 1 is a four-in-one-type module that houses four sets of semiconductor switching devices T1 through T4 in a package. Each of switching devices T1 through T4 includes an IGBT and an FWD connected in opposite parallel to each other. Two sets of semiconductor switching devices T1 and T2 are connected in series to each other between the positive terminal P and the negative terminal N of a DC power supply such that an upper arm and a lower arm for one phase are formed. Two sets of semiconductor switching devices T3 and T4 are connected in opposite series to each other and, then, connected between the AC output terminal U and the neutral point terminal M such that a bidirectional switching circuit for clipping is formed.
The positive terminal P of IGBT module 1 and the neutral point terminal of capacitor 4 are connected to each other via conductor 3P. The negative terminal N of IGBT module 1 and the neutral point terminal of capacitor 4 are connected to each other via conductor 3N. The neutral point terminal M of IGBT module 1 and the neutral point terminal of capacitor 4 are connected to each other via conductor 3M. Since the operations of the three-level IGBT module and the functions of laminated bus bar 3 are described in detail in Patent Documents 1 and 2, their descriptions are not made here.
In FIG. 6 that illustrates the external appearance of the module, main circuit terminals (P, N, U, M) 7 of IGBT module 1 are aligned on convex terminal board 5a formed on the upper surface center of molded resin casing 5. Control terminals 8 such as gate terminals led out from the respective sets of switching devices T1 through T4 are spaced apart from main circuit terminals 7 and arranged on terminal board 5b formed on the side edge area of molded resin casing 5.
Now, the conventional structure of laminated bus bar 3 employed in the inverter unit described above and connected to inverter module 1 will be described below with reference to FIGS. 4(a), 4(b), and 7. Laminated bus bar 3 is a structure formed of plate-shaped conductors 3P, 3N, and 3M corresponding to the main wiring circuits shown in FIG. 5 and insulator plates 3a. Conductors 3P, 3N, and 3M and insulator plates 3a are laminated into a sandwich-shaped unit. Terminal sections connected to main circuit terminals 7 on IGBT module 1 are patterned as described below in respective conductors 3P, 3N, and 3M.
As described by portion A in FIG. 4(a), right and left concave terminal-leading-out-windows 3b are formed separately in the right-hand-side-portion and the left-hand-side-portion of insulator plates 3a in the end section of laminated bus bar 3 corresponding to terminal boards 5a of two IGBT modules 1, respectively. In accordance with the arrangement of main circuit terminals 7 of IGBT module 1, connection terminal sections 3P-1, 3N-1, and 3M-1 are led out into terminal-leading-out-window 3b. Through holes 3c for terminal screws (not-shown) bored through the connection terminal sections 3P-1, 3N-1, and 3M-1 are shown in FIG. 4(b). The led-out-sections of the conductors are bent appropriately in concave and in convex so that the central portions in the respective connection terminal sections of the conductors may be aligned in a plane.
In connecting laminated bus bar 3 to IGBT module 1, terminal-leading-out-windows 3b in laminated bus bar 3 are positioned on terminal boards 5a of IGBT modules 1 and connection terminal sections 3P-1, 3N-1, and 3M-1 of conductors 3P, 3N, and 3M and main circuit terminals 7 of IGBT modules 1 are joint to each other with terminals screws (not shown). Capacitors 4 are mounted on the far side of window 3b (the lower end side of laminated bus bar 3 in FIG. 4(a)) and connected between conductor 3M and conductors 3P and 3N.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-22062
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2008-193779
The Standards of the Japan Electrical Manufacturers' Association (hereinafter referred to as the “JEM Standards”) and the Standards of the International Electro-technical Commission (hereinafter referred to as the “IEC Standards”) provide the domestic and international guidelines for the insulation performances of the electric equipment such as inverters. The JEM Standards and the IEC Standards specify the creepage distance and clearance distance for insulation corresponding to the kinds of the equipment, environments (degrees of contamination), and operating voltages. Especially, on the electric equipment for the rolling stock, the annex of the International Standard IEC 60077-1 (Railway applications—Electric equipment for rolling stock; hereinafter referred to simply as the “International Standard IEC 60077-1”) specifies the insulation distances (creepage distance and clearance distance) as the persons skilled in the art well know.
As for the insulation, trenches 5a-1 are formed, as shown in FIG. 6, between main circuit terminals 7 and across terminal board 5a in the product of IGBT module 1 to secure the required creepage distance and clearance distance following the Standards described above. As for laminated bus bar 3 to be assembled to IGBT module 1, connection terminal sections 3P-1, 3N-1, and 3M-1 are led out from conductors 3P, 3N, and 3M to be connected to main circuit terminals 7 of IGBT module 1. Connection terminal sections 3P-1, 3N-1, and 3M-1 are led out from the spaces between insulator plates 3a and arranged in terminal-leading-out-window 3b in accordance with the arrangement pitch of main circuit terminals 7.
In the conventional laminated bus bar 3 structure (cf. FIG. 7), connection terminal sections 3P-1, 3N-1, and 3M-1 of the conductors sandwiched between insulator plates 3a are led out such that connection terminal sections 3P-1, 3N-1, and 3M-1 are separated from each other along the parallel edges of terminal-leading-out-window 3b cut linearly and extended in perpendicular to the linear edges of terminal-leading-out-window 3b. Therefore, the creepage distance between connection terminal sections 3P-1, 3N-1, and 3M-1 is the linear distance (the same with the clearance distance) along the cut edges of insulator plates 3a as schematically shown in FIG. 8.
However, the linear creepage distance is shorter than the creepage distance via the inner surface of trench 5a-1 formed between main circuit terminals 7 and across terminal board 5a on IGBT module 1 (cf. FIG. 6). Therefore, it is difficult for laminated bus bar 3 having the conventional structure to secure high insulation performances. If the inverter unit is applied to the electric power converters on the rolling stock, it will be difficult for laminated bus bar 3 having the conventional structure to follow the International Standard IEC60077-1 due to the shortage of the creepage distance between the connection terminal sections.
In view of the foregoing, it would be desirable to obviate the problems described above. It would be also desirable to provide a laminated bus bar that facilitates elongation of the creepage distance between the conductor terminals thereof by a few work applied to the insulator plates such that the creepage distance follows the International Standard and the insulation performances thereof are improved.
Further objects and advantages of the invention will be apparent from the following, description of the invention.